In insider jargon among fireworks professionals a "birthday cake" or more briefly just a "cake" is a firework technically referred to as a "multi-shot tube device." These are fireworks that consist of multiple, usually small mortar tubes bundled together designed to fire a series of low-level aerial effects. The effects might be stars, comets, whistles, salutes, etc.

"Let's set those birthday cakes up over on the left of the firing line."